The area Within Earthen Peak Ruins follows on from the Earthen Ruins section of the Ringed City DLC, with plenty of challenges, including the two Demon in Pain and Demon From Below bosses, and the Demon Prince boss, lying ahead. If you need help with other parts of the DLC meanwhile, then take a look at our Dark Souls 3: Ringed City guide and walkthrough hub for plenty more.
How to beat the Demon in Pain and Demon From Below bosses
From the bonfire, if you've followed this guide, you should be able to summon Lapp nearby, assuming you're embered. Now step out onto the farthest edge of the toppled structure and look down. Yep, you need to drop all the way down there. Off you go. Down here you'll face your first boss.
Your first boss encounter in Ringed City is actually two bosses. They're both very similar in their attack patterns. If you see either of them arching up for an attack, roll. Try stay close, and just keep chipping away. Try not to get too greedy with hits, but be sure to take advantage any time the embers die out on them, as you can get in some extra hits while they're in this state.
How to beat the Demon Prince boss
Once they're both down, it's time to face the Demon Prince. It's a similar fight, though sometimes this one will jump upwards, taking flight - when it does this, roll towards it, away from its projectiles. Its most devastating attack is when it rains fireballs, but it's really hard to judge when this is coming, so try to save some Estus for this final form. Rolling like you're actually on fire helps. If Lapp's still with you at this point, it's a pretty easy fight.
After the fight, rest at the bonfire, then head through the room nearby and collect the Small Envoy Banner key item from a corpse, before heading down into the depths. Use the Small Envoy Banner at the edge and you'll be flown to a new area.
When you land, look behind you and grab the Titanite Scale nestled there. Head downwards, talk to the NPC nearby, then rest at the bonfire. Welcome to the Ringed City: next up it's the Mausoleum Lookout.